As processes of manufacturing inorganic nanofibers by electrospinning, a process in which a precursor solution containing a metal alkoxide and an organic polymer is sintered after spinning, and a process in which a spinnable sol solution prepared from a metal alkoxide without using an organic polymer is spun, are known.
The process in which a precursor solution containing a metal alkoxide and an organic polymer is used for spinning is disclosed in, for example, non patent literature 1 and patent literature 1. A disadvantage of this process is that the obtained fibers are very brittle. This is because the precursor solution contains a large amount of the organic polymer to fiberize the precursor solution, and thus, many micropores are formed in the inorganic nanofibers obtained after sintering.
The process in which a spinnable sol solution is spun is disclosed in patent literature 2. In this invention, because the sol per se, which is used as a spinning material, is spinnable, an organic polymer is not needed, and thus, a nanofiber sheet strong enough to be handled can be produced. Although a process of manufacturing silica nanofibers was referred to in the invention disclosed in patent literature 2, a process of preparing a spinnable sol using a highly reactive metal alkoxide such as titanium alkoxide or zirconium alkoxide was not referred to.